Drive belt

Updated: September 13, 2013
Serpentine belt
V-ribbed drive belt. BMW engine.
Click for larger image.

A drive belt or serpentine belt drives accessories installed on your engine, such as the alternator, water pump, power steering pump and the air conditioner compressor. Modern cars typically have one or two drive belts. Older cars used V-shaped belts, while modern cars use V-ribbed belts that are flat on one side and have ribs on the other side. A drive belt is made from a very durable material, but it still wears over time. On average, a drive belt can last for 3-4 years. Improper tension, excessive heat, oil or coolant leaks cause the drive belt to wear faster. A worn out belt may cause squeaking or chirping noises and a badly worn-out belt can break.

What happens if the drive belt breaks

Water pump driven by a drive belt

If the drive belt breaks, the engine might overheat as the water pump will stop circulating coolant into the radiator to cool it down. The battery light might come on on the dash because the alternator will stop charging the battery. A car with a hydraulic power steering might also lose the steering assist, so the steering will become very stiff. All in all, if a drive belt breaks, you won't be able to drive your car.

Drive belt noises

Water pump driven by a drive belt

A worn-out drive belt, like in the photo, can cause chirping or squeaking noise that is usually more noticeable after driving in the rain. This happens because water gets on the belt and washes off the dust. This type of noise can also be caused by misalignment of the belt pulleys.
A loose drive belt can slip causing a loud high-pitch squealing or whistling noise. Usually you can hear it when the engine is just started or when the steering wheel is turned to the limit in either side. It is a fairly simple job to adjust the drive belt tension, so it should not cost you a lot when you take your vehicle to a mechanic. Driving with a loosened drive belt can cause many other problems, e.g. low battery charge, overheating, lack of power-steering assist, etc.

When the drive belt needs to be replaced

Cracked drive belt

A drive belt needs to be checked regularly and replaced at recommended intervals; typically every 40,000-60,000 miles. If during a regular service, your mechanic found that the belt shows signs of wear, such as cracks (as in this photo), cuts, or tears, it's better to have the belt replaced. It's also a good idea to replace an old drive belt before a long road trip. Read more: Car checklist before a long trip.

Drive belt tensioner

Serpentine belt tensioner

Over time, the drive belt stretches. To compensate for this there is a belt tensioner that keeps the drive belt under proper tension. In some older cars, a belt tensioner had to be manually adjusted from time to time. Newer cars have a drive belt with a spring-loaded self-adjusting tensioner that maintains the proper belt tension automatically.

Drive belt replacement

A drive belt is not very expensive part and usually doesn't cost much to replace. Roughly, a drive belt replacement in a garage could range from $90 to $180. On most cars it's a fairly simple job that typically takes no more than 30-40 minutes. If you want to replace a drive belt yourself, you will need a drive belt diagram. One way to get it is to draw a diagram from the existing belt.

Q: After my alternator was changed, my drive belt was making a chirping noise. I have changed the belt with a new one recently but it still makes the same noise, although it's not as loud as before.

A: If you said that the noise started after the alternator has been replaced, we would recommend to recheck the alternator installation. The noise you describe could happen when the belt pulleys are not aligned properly. Maybe the alternator was not installed correctly or the belt pulley on the alternator is not seating properly.

Q: In my 2003 Corolla I can hear the rattling noise from the passenger side of the car when I start it cold. I have changed my drive belt a year ago, could it be bad again?

A: It could be a failing belt tensioner which was a common problem in this car. Have it checked out.

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